You can do a lot to improve your iPhone's battery life, but sometimes you just get a bad app that will suck up your battery all on its own. Here's one trick we've discovered for finding out which app that is.

Tell me if this has happened to you before: you're using your iPhone, and everything is fine until you realize that the location services icon in your menu bar is on even when you aren't using something like Maps. There are a few apps out there that just keep location services on 24/7, even when the app isn't open.

To figure out which one it is, just open up your Settings app, go to Location Services, and search for a purple arrow in the list. The app with the purple GPS arrow indicates which app is currently using your location services, and if it's something you didn't turn on yourself (like navigation, for example), that app is probably the one sucking up your battery. You can either turn location services off or see if there's setting within the app that fixes the problem.

This may seem obvious to some, but it's happened to a bunch of us here at Lifehacker, and it took us a while to figure out how to solve the problem. If you're noticing that your battery isn't lasting very long, this is a good trick to try. Of course, you could also use something like previously mentionedCarat to find the offending app, if this doesn't help.